1. Field of the Invention
This invention relates generally to seal members, and is particularly concerned with piston rod wiping or scraping seal members for cleaning dust and other foreign matter from reciprocating piston rods as the rod enters a cylinder chamber to prevent contamination of the chamber.
2. Description of the Prior Art
A particular problem that occurs with piston and cylinder assemblies is that of preventing contamination of the chamber formed between the piston head and the end wall of the cylinder. As the piston reciprocates within the chamber, the piston rod moves in and out of the chamber. Dust and other foreign matter can collect on the surface of any portion of the piston rod externally of the chamber. When the rod moves back into the chamber on a return stroke, the dust and other foreign matter must be cleaned from the surface of the rod. If it isn't, the foreign matter may not only enter the working chamber within the cylinder, but can damage the seal or packing assembly surrounding the piston rod in the end wall of the cylinder.
It is conventional to mount in a groove in the end wall of the cylinder a scraping or wiping seal member of resilient material (sometimes also referred to as excluders) for wiping or scraping dust and other foreign matter from the surface of a piston rod on an inward stroke of the piston.
Among the problems associated with such rod wiping seals is providing a construction that can be easily installed and removed, and one that will stand up under adverse operating conditions without an unacceptable failure rate.
Another problem with prior art rod wiping seals is that premature failure of the seal frequently results from the accummulation of dirt and other foreign matter between the walls of the packing housing and the wiping seal. The accummulated dirt forces the wiper toward the rod which results in excessive friction between the rod and wiping seal. Furthermore, when the bearings used to maintain alignment of the rod wear, transverse movement of the rod results. This increases the likelihood of dirt and foreign matter entering the cylinder between the surfaces of the packing housing and the wiping seal because of the transverse forces tending to cause distortion of the wiping seal when the rod moves transversely.